How do fuel cells differ from batteries in the way they produce electricity?

While both fuel cells and batteries are electrochemical devices that convert chemical energy directly into electricity using electrodes and an electrolyte, they differ fundamentally in how they produce that energy.12

• Source of Reactants: A battery contains a limited, fixed amount of fuel material and oxidant stored internally. As the battery operates, these materials are depleted, eventually requiring the battery to be recharged or replaced. In contrast, a fuel cell is an open system that is continuously supplied with fuel (such as hydrogen) and an oxidizer (such as oxygen) from an external source.21
• Longevity and Operation: Because fuel cells are continuously supplied with reactants, they can generate electricity for as long as that supply is maintained. The electrodes and electrolyte in a fuel cell are designed to remain unchanged by the chemical reactions, whereas the internal components of a battery undergo chemical transformations that are consumed or altered during use.1

Essentially, a battery acts as an energy storage device, while a fuel cell functions more like an energy conversion system.12